First day of the new year, celebrated with religious, cultural, and social observances around the world. It is usually marked by rites and ceremonies that symbolize casting off the old year and rejoicing in the new. Most of the world recognizes January 1 as the start of a new year because the Gregorian calendar, from its papal origin in 1582, has become the international reference for treaties, corporate contracts, and other legal documents. Nevertheless, numerous religious and national calendars have been retained. For example, in the Persian calendar (used in Iran and Afghanistan) New Year's Day falls on the spring equinox (March 20 or 21 in the Gregorian calendar). The more widely employed Islamic (Hijri) calendar is based on 12 lunar months of 29 or 30 days; thus, the Islamic New Year's Day gradually regresses through the longer Gregorian calendar. The Hindu new year starts on the day following the first new moon on or after the spring equinox. The Chinese new year begins at sunset on the new moon in the sign of Aquarius (late January or early February). The Hebrew calendar is based on 12 lunar months (13 in certain years) of 29 or 30 days; the Jewish New Year's Day, or Rosh Hashanah, can fall anytime from September 6 to October 5 in the Gregorian calendar.